There are some cold-blooded reasons to rob, assault, or kill somebody, but few seem harsher than harming an acquaintance or even an innocent stranger just to test the method a criminal plans to use on their real desired target.
Sometimes The Chessmaster's plans are so complex and convoluted, it becomes necessary to test how they work. Or perhaps they simply like being prepared. The saying is that no plan survives contact with the enemy, so running it against a real person will help discover the problems like any beta testing.
Sure, the criminal could do a simulation...maybe...but for whatever reason, they've chosen a practice crime instead.
When the crime in question is murder, this trope will most likely constitute a Moral Event Horizon crossing.
Compare Trial Balloon Question (a related but much more innocuous trope) and Serial Killings, Specific Target (another heinous trope involving secondary killings intended to aid a primary murder). Often combined with Tested on Humans.
- Light does this several times in Death Note:
- His first victim is a man holding children hostage in a school. As the news cuts off before he can see exactly what happened, he isn't convinced.
- He next uses the Death Note on a man harassing a woman outside a convenience store. He's also able to test the "cause of death" clause by specifying the man die in an "accident" — he gets hit by a truck.
- Realizing the Note works, and with L on his trail, he begins testing the Note by having prisoners do things just before dying. He's specifically looking for limits on what they can and cannot do before dying.
- When L gets the Death Note, he wants to have a death-row convict test the 13-day rule. L dies before he can put this plan into action.
- Suicide Squad #1 opens with Terrorists Without a Cause the Jihad staging an attack on an airport to assassinate the US President, and causing massive civilian casualties in the process. It turns out the airport is a mockup and all of the murdered people actors, with this being a test by the Quraci of whether the team was ready to be sent into the field.
- The terrorist group Black September from the film adaptation of the Thomas Harris novel Black Sunday recruits deranged Vietnam vet Lander to develop an anti-personnel weapon, to be used against the President while he attends the Super Bowl. Lander builds a large Claymore mine, and field tests its killing power by convincing a farmer that it's a new television camera. The poor fellow stands still, smiling, when the device goes off, riddling the entire side of his barn with holes. It may be presumed the farmer was liquefied where he stood. The terrorists then plan to install these devices on the exterior of the Goodyear blimp, which will likely kill the President and thousands more in attendance.
- In The Jackal, Bruce Willis's assassin character does this, killing the arms dealer who sold him his high-powered gun with that gun, to make sure that it will work when used on his target.
- Crime and Punishment has a variation. Raskolnikov kills a moneylender who won't be missed, mostly to prove to himself that he's an ‹bermensch and smart enough to get away with the crime. But he doesn't have any concrete plans for a larger crime afterwards, just vague ideas about reshaping the world with his will.
- Sherlock Holmes : In "Silver Blaze", Holmes asks a person taking care of sheep if there was anything wrong with them lately. Turns out a few went lame. This confirms Holmes' suspicion the supposed murder victim was trying to cripple the eponymous horse after betting against it, and the sheep were used for practice. There was no murder; the horse merely caved the man's skull in during the preparation for the real crime.
- The first murder in the Hercule Poirot novel Three Act Tragedy turns out to be this, with the killer wishing to test if their scheme for switching glasses during a crowded party would work.
- In a meta sense, many of the murder methods used in Agatha Christie's novels are recycled from her short stories (e.g. the philandering husband and downtrodden wife who clearly hate each other actually being partners in crime in Triangle at Rhodes and Evil Under the Sun) as a trial run to see if any readers complained of the plot's implausibility.
- In Orson Scott Card's The Worthing Saga, inhabitants of the City Planet Capitol (capitol of The Empire), play an elaborate Civilization-style massively-multiplayer historical civilization-building game as a sort of spectator sport. One player, a genius named Herman Nuber, creates a Hegemonic Empire so powerful yet so beneficent and internally stable that he looks certain to Take Over the World of the game and end it in a permanent Pax Nubera. Before he can do so, Abner Doon (who turns out to be Nuber's grandson) buys out Nuber's place and undermines his empire so completely that not only does it fail to conquer the world, it is eradicated completely by universal simultaneous rebellion. Doon reveals that he considers this a trial run; he intends to do the same thing to The Empire in real life. Interestingly, while destroying Nuber's in-game empire is not technically a crime (just a supreme dick move), Doon expresses much more remorse for that than for destroying the actual Empire, saying that he did not realize what a toll it would take on his grandfather's mental health to see his life's work destroyed.
- In the The Blacklist, a SVR assassin named Karakurt runs a test to see if he can kill someone with a virus through touching someone. The FBI is baffled on why a college student was targeted until they find out that he's suppose to target an anti-Russian politician and even if that doesn't work, one of his contacts uses the virus so that the Alliance/Cabal can use Liz as a stooge.
- An episode of Criminal Minds had the BAU hunting down an apparent serial poisoner that had killed various people around town. After some investigation, they discovered that the poisoner had placed his poison in the glue of some stamps (which he then placed on the local post office), and he had done this to test the way through which he was going to kill all of his co-workers (that were pissing him off) in a corporate team-building meeting.
- CSI: NY:
- "Love Run Cold" has the detectives discover that a cat whose owner lives near the suspect was poisoned in the same way as the Victim of the Week (using a substance said suspect uses to prepare food she's photographing) and that the cat's owner suspects she did it.
- The perp in "Point of View" poisons a canary as well, but he's preparing for a mass murder.
- Doctor Who:
- "Journey's End": Davros tests his "reality bomb" on a group of unlucky civilians abducted from Earth before magnifying it with the intention of using it to rip apart the entire multiverse.
- "Kerblam!": It turns out the titular company's missing employees were abducted by the villain to test the bubble wrap bombs he planned to use to kill thousands of customers.
- In an episode of Hawaii Five-O, would-be terrorists want to introduce a weaponized Ebola-like illness to the population using bees. They lure a random Island dude to their remote location with the phony promise of a job interview, and then lock him in the room and flood it with infected bees to make sure they can effectively spread the disease (and that the disease will have its intended quick-kill effect).
- In an episode of Leverage, during a job recovering a stolen painting, the team encounters a group of thieves who get the painting before them. They discover that the thieves were put together by an old grifter associate of Sophie's, Starke. Starke's M.O. is basically to form a one-shot team and have them do one job as a practice run, presumably to make sure they can work together, before going after his real target. The stolen painting was the practice run, so the Leverage team have to figure out what Starke is after first and get it before him in order to get the stolen painting back.
- One episode of Lois & Clark involved numerous headless bodies being found all over Metropolis. Turns out a millionaire with a disfigured body intended to transplant his head onto Superman's body and the doctors were testing the technique.
- The Professionals: In the episode "Killer With A Long Arm", a Cold Sniper hired for an assassination sights in his custom-made rifle on a scarecrow, but is witnessed and has to flee the scene without checking the zero. So the second time he tests the rifle by gunning down a man on a golf course. If there was a reason for him to use a live target other than just to be a dick, it was not adequately explained.
- In an episode of Psych, Spencer deduces that the robbery of an ice-cream truck was a test run for the planned robbery of an armored car using the same method.
- In the Sherlock episode "The Sign of Three", the first victim is a Buckingham Palace guard found near death from a stab wound with no weapon in sight, in a locked-room mystery. Turns out that the killer had attempted to kill him for no other reason than to test a method intended to be used on another victim. The "test" victim lived (because Watson was there to give him medical treatment). It was a plot point, since it made it clear that Watson would be able to save the second victim (his old friend and wedding guest).
- In Embers in the Dusk, in the aftermath of Garkill's final invasion, a Defence Cruiser was destroyed during the cleanup bombardments (crit fail). Later, it turned out Chaos Psykers were working out a way to teleport past ship shields. When you discover them, they're aboard your flagship and have taken control of your fleet commander.
- In strip #906 of The Order of the Stick, this is the motive Nale gives for murdering Malack's vampire "children".
- Supposedly some samurai would test out a new blade by going out and killing a random commoner with it (as opposed to criminals or dead bodies).
- Richard Kuklinski, "The Iceman Killer", allegedly committed several murders purely to practice a new method he planned to use for a later contract killing; amongst other things, he supposedly poisoned random restaurant customers and killed a man with a crossbow.
- A British armed robber claimed that early in his career he went out to a farm and shot a random cow, reasoning that if he could kill an animal then he would be capable of killing a human being if he ever felt forced to do that (which, luckily, never happened).